1. Field of the Invention
This invention relates to preparations comprising modified alkali metal silicate solutions for sealing and/or stabilizing and/or binding, to the use of these preparations, and to a process for sealing and/or stabilizing and/or binding using these preparations.
Preparations based on aqueous alkali metal silicate solutions have long been known and are widely used in practice, for example in the stabilization and sealing of ground and soils. In tunnel construction and underground railway construction, for example, alkali metal silicate solutions are injected into the ground to stabilize the soil and to underpin already erected buildings and to stabilize the ground. In addition, aqueous alkali metal silicate solutions may be used for stabilizing building materials and masonry and as a binder for moldings consisting of minerals.
Where alkali metal silicate solutions are used without additives, they are often unable to satisfy technical requirements. Thus, hardness, elasticity and resistance to temperatures and water are frequently inadequate. Because of this, numerous proposals have already been put forward with a view to improving the properties of alkali metal silicate solutions. In particular, hardeners of various kinds, for example, glyoxal or dicarboxylic acid esters, have been used.
2. Description of Related Art
France Patent No. 1,166,581 describes the use of glyoxal as a hardener for alkali metal silicate solutions. Unfortunately, the rapid reaction between concentrated alkali metal silicate solutions and the glyoxal seriously restricts potential applications.
It is also known that the reaction velocities of alkali metal silicate solutions containing hardeners can be reduced as required by dilution with water, i.e., by reducing their solids content. Unfortunately, this gives rise to the disadvantage that, for example, the stabilization of soils and/or mineral building materials and molding materials is not sufficient so that potential applications are seriously restricted again.
U.S. Pat. No. 4,293,340 describes soil-stabilizing preparations containing aqueous alkali metal silicate solutions, glyoxal and hydrogen peroxide and, optionally, inorganic salts. The inorganic salts used are those belonging to groups I to III, more especially sodium aluminate, aluminium chloride, copper sulfate, zinc chloride and calcium chloride, calcium chloride being preferred. However, soil stabilized with preparations such as these shows inadequate compressive strength.
U.S. Pat. No. 3,493,406 describes a process for stabilizing soils using an aqueous silicate solution containing an addition of a gel-forming agent. The gel-forming agent used is a mixture of succinic acid dialkyl ester with dialkyl esters of homologous higher carboxylic acids, such as glutaric acid and/or adipic acid. The disadvantage of preparations such as these is that, after they have been introduced into the soil, ground waters and soil are polluted by large quantities of organic substances which have to be degraded. This type of pollution is measured as "chemical oxygen demand" (COD-value).
U.S. Pat. No. 4,171,986 describes binders based on alkali metal silicate solutions having a reduced setting time and improved water resistance. These binders based on alkali metal silicate solutions with a molar ratio of SiO.sub.2 to Me.sub.2 O of from 1.8 to 4.0 and a solids content of from 20 to 55% by weight are characterized by a content of potassium metaborate, the molar ratio of SiO.sub.2 to potassium metaborate being in the range of from 0.1 to 50. However, the advantages obtainable with binders such as these, i.e., the high water resistance and, in particular, the increased setting rate, cannot be obtained with sodium metaborate, as can be seen from Example 1 and Comparison Examples E and F described in German Application No. 27 14 889.
The problem which the present invention seeks to solve is to eliminate the above-mentioned disadvantages of the prior art by modifying the alkali metal silicate solutions and, in particular, to provide alkali metal silicate solutions which have sufficiently long gelling times and hardening times for practical application, even at high solids contents.
According to the invention, this problem is solved by the provision of sealing, stabilizing and binding agents comprising modified alkali metal silicate solutions.